Definition: Mechanical devices used to safely collect and manage the primary guideline as well as ensure that there is a continuous guideline from the surface to the end of the dive; One of the most important cave devices carried by individual and team cave divers.
“You will be in-charge with carrying the line reels. It is necessary for keeping our primary lines intact.”
Source: http://www.swiss-cave-diving.ch/Lexica/BasicCaveDivingTerms_London.html